FIG. 1 shows a conventional twin roll casting machine based on an invention disclosed in JP-8-300108A.
This twin roll casting machine comprises a casting module 3 with a pair of chilled rolls 1 adapted to continuously cast a strip 2, a pair of pinch rolls 4 for pinching the strip 2 from the chilled rolls 1 to feed the same to a succeeding process such as rolling, an enclosure 5 with an open lower end for enclosing a transfer path of the strip 2 from the casting module 3 to the pinch rolls 4, a scrap box 7 with an upper-end opening confronting the lower-end opening of the enclosure 5, said scrap box being vertically movable by jacks 6, and a sledding table 8 and a plurality of table rolls 9 arranged within the enclosure 5.
The casting module 3 has a pair of side weirs 10 abutting on one and the other ends of the chilled rolls 1, respectively, a sealing chamber 11 under the chilled rolls 1 for surrounding the transfer path of the strip 2 and sealing members 12 contiguous with an upper end of the sealing chamber 11 to abut on outer peripheries of the chilled rolls 1.
The chilled rolls 1 are horizontally arranged in parallel with each other, a nip between the rolls being adjustable to be selectively increased or decreased depending upon thickness of the strip 2 to be cast.
Rolling directions and velocities of the chilled rolls 1 are set such that the outer peripheries of the rolls are moved from above toward the nip at the same velocity.
The chilled rolls 1 are structured such that cooling water may pass through the rolls.
Molten metal is fed to a space defined by the chilled rolls 1 and the side weirs 10 to form a molten metal pool 13.
Formation of the molten metal pool 13 and rotation of the rolls 1 which are being cooled cause the metal to solidify on the outer peripheries of the chilled rolls 1 so that the strip 2 is delivered downward via the nip.
The pinch rolls 4 are arranged downstream of the chilled rolls 1 and adjacent to a succeeding process to which the strip 2 is to be delivered.
An upper end of the enclosure 5 provides a sealing chamber 14 into and from which a lower end of the sealing chamber 11 of the casting module 3 may be inserted and withdrawn.
A sealing member 15 is arranged between a vertical wall of the sealing chamber 14 and a lower vertical surface of the sealing chamber 11 of the casting module 3 and is in surface contact wholly with peripheries of these sealing chambers 11 and 14.
A downstream portion of the enclosure 5 in a direction of travel of the strip 2 is provided with sealing members 16 abutting on outer peripheries of the pinch rolls 4.
A peripheral edge of the upper-end opening of the scrap box 7 is provided with a sealing member 17 which may be in surface contact wholly with a peripheral edge of the lower-end opening of the enclosure 5 when the scrap box 7 is lifted up by the jacks 6.
This scrap box 7 is provided to withdraw any shape-defective strip 2 produced upon initial phase of a casting operation.
Inert gas (nitrogen gas) G is fed through a conduit 18 into the casting module 3, the enclosure 5 and the scrap box 7 so as to maintain interiors of the same in non-oxidative atmosphere for prevention of the hot strip 2 from oxidization.
The inert gas G is restrained from flowing outside by the sealing members 12 and 16, respectively, between the sealing chamber 11 and the chilled rolls 1 and between the enclosure 5 and the pinch rolls 4.
The sledding table 8 is adapted to take two alternative postures, one for guidance of the strip 2 from the chilled rolls 1 to the pinch rolls 4 and the other not in contact with the strip 2.
The sledding table 8 is arranged to support from below the strip 2 passing via the table rolls 9 to the pinch rolls 4.
However, in the twin roll casting machine shown in FIG. 1, atmosphere temperature in the enclosure 5 may rise under the influence of the hot molten metal pool 13, resulting in thermal deformation of the sealing chambers 11 and 14, the enclosure 5 and the scrap box 7.
This causes the sealing members 15 and 17 not to be in surface contact wholly with the outer periphery of the sealing chamber 11 and wholly with the peripheral edge of the lower-end opening of the enclosure 5, so that the inert gas G to be charged in the casting module 3, the enclosure 5 and the scrap box 7 is allowed to flow outside and ambient air flows into the enclosure 5 and the like in an amount corresponding to that of the inert gas G having flowed outside.
Therefore, the enclosure 5 must be replenished with inert gas G in an amount corresponding to that of the inert gas G having flowed outside so as to prevent the strip 2 from being oxidized.
The present invention was made in view of the above and has its object to provide a twin roll casting machine which can reduce an amount of inert gas supplied for prevention of the strip from oxidization.